1. Field of the Invention
The present invention relates to an optical near-field generator and a recording and reproducing apparatus using the same.
2. Background Art
In recent years, a thermally assisted magnetic recording system has been proposed as a recording system which realizes a recording density equal to or larger than 1 Tb/in2 (H. Saga, H. Nemoto, H. Sukeda, and M. Takahashi, Jpn. J. Appl. Phys. 38, Part 1, 1839 (1999)). In a conventional magnetic recording apparatus, when a recording density thereof is equal to or larger than 1 Tb/in2, loss of recorded information due to thermal fluctuation becomes a problem. In order to prevent this problem, it is necessary to increase a coercive force of a magnetic recording medium. However, the magnitude of a magnetic field which can be generated from a magnetic recording head is limited, and hence if the coercive force is excessively increased, it becomes impossible to form recording bits on the medium. In order to solve this, in the thermally assisted magnetic recording system, the medium is heated with light at the moment of recording, to thereby reduce the coercive force. This enables recording on the medium having a high coercive force, and makes it possible to realize the recording density equal to or larger than 1 Tb/in2.
In this thermal assisted magnetic recording device, it is necessary to set a spot diameter of radiated light to a value (several 10 nm) nearly equal to the recording bits. This is because the light erases information in an adjacent track if the spot diameter of the light is larger than this value. In order to heat such a minute region, an optical near-field is used. The optical near-field is an electromagnetic field (light whose wavenumber has imaginary components) which is localized in the vicinity of a minute object equal to or smaller than a light wavelength, and is generated by using a minute opening or a metal scatterer having a diameter equal to or smaller than the light wavelength. For example, JP 2001-255254A proposes an optical near-field generating element which uses a metal scatterer having a triangular shape, as a highly efficient optical near-field generating element. When light is caused to enter the metal scatterer, plasmon resonance is excited in the metal scatterer, so that a strong optical near-field is generated at a vertex of the triangle. The use of this optical near-field generating element makes it possible to highly efficiently collect the light in a region equal to or smaller than several 10 nm. In addition, JP 2004-151046A proposes a structure in which a recess is formed in a portion other than the vertex at which the optical near-field is generated, on a surface of the metal scatterer on an air bearing surface side. This structure makes it possible to reduce the width of intensity distribution of the optical near-field generated at the vertex, and to suppress the occurrence of a weak optical near-field (background light) generated around the opposite side to the vertex.
For the thermally assisted magnetic recording system described above, it is necessary to heat with light the vicinity of a magnetic pole for applying a magnetic field. For this purpose, for example, a waveguide is formed beside the magnetic pole, and the light generated from a semiconductor laser as a light source is guided to the vicinity of a leading end of the magnetic pole. At this time, the semiconductor laser is mounted on the floating slider or is placed at a base of a suspension, and the light is guided therefrom to the floating slider by using the waveguide such as an optical fiber.
As the method of placing the semiconductor laser as the light source on the floating slider, for example, US 2009/0266789A1 proposes a method in which an edge emitting laser is placed so as to stand perpendicularly on an upper surface of the floating slider. In addition, JP 2009-4030A proposes a method in which the semiconductor laser is placed so as to be horizontal to an upper surface of the floating slider, and a mirror is formed on an end surface thereof, to thereby couple emitted light directly to a waveguide formed in the floating slider.
In addition, US 2008/0002298A1 proposes a method of placing the semiconductor laser on a side surface of the slider. In this case, a vertical cavity surface emitting laser is used as the semiconductor laser, and the laser is placed on the side surface of the floating slider on a trailing side. The slider includes a waveguide having a side surface on which a grating coupler is formed, and the light emitted from the semiconductor laser is coupled to the waveguide via the grating coupler.